There is a need in many RF systems to provide an orthogonal transition from a microstrip transmission line to a coaxial transmission line. A known technique of accomplishing this is to end launch a right angle coax connector onto microstrip along the substrate edge. Disadvantages of this approach include the relatively large space and volume requirements, and the requirement that the transition be made at the edge of the substrate.
It would therefore be an advantage to provide a transition technique which required less space, and offered the flexibility to vertically launch anywhere along the microstrip circuit board.
Another problem not addressed by known transition techniques between coaxial and microstrip transmission lines involves the issue of complete ground shielding the coaxial launcher as it contacts the microstrip center conductor vertically from an air dielectric side. In known techniques, the coaxial outer ground shield is partially removed to prevent that shield from short circuiting the microstrip center conductor. Exposing the coaxial section to air will result in RF leakage and the generation of the higher order waveguide modes, and thus degrades the RF performance when used at higher frequencies. Commercially available coaxial launchers are thus limited at the high frequency end to about 7 Ghz. Launchers for channelized microstrip transmission line described in U.S. Pat. No. 5,416,453 are limited at the high frequency end to about 14 Ghz.